Journal of the Geological Society, London, Vol. 147, 1990, pp. 725-728, 7 figs. Printed in Northern Ireland Further evidence for diversity in late Silurian land vegetation U. FANNING',D. EDWARDS' & J. B. RICHARDSON* l Department of Geology, University of Wales College of Cardiff, Cardiff CFl3YE, UK 'Department of Palaeontology, British Museum (Natural History), London SW75BD, UK Abtraet: Small coalified plant fragments from basal Pridoli (Silurian) strata at Perton near Hereford, England comprise isotomously branching smooth axes terminating in vertically elongate sporangia. The latter, whichoccasionally bifurcate, arecharacterized by prominent, distally concentrated, spinous emergences and contain trilete, retusoid, smooth-walled isospores. The plants are placed in a new genus and species, Caia langii. Comparisons are made with a number of Silurian and Lower Devonianplants with elongate sporangia and particularly with Horneophyton. A hypothesisis developed that spines on sporangia had a nutritive function. The spores are discussed in terms of other records of late Silurian-Early Devonian in situ spores. It is not without irony that the very strata in Wales and the Systematic palaeobotany Welsh Borderland that Roderick Murchison insisted were devoid of plants have yielded the most extensive record to Incertae sedis date of early land vegetation. The exposure in the Downton Genus CAIA gen. nov. Group of Perton Lane near Hereford was not visited by Murchison, but is now well known to palaeobotanists as the Type species. Caia langii sp. nov. type locality of the genus Cooksonia Lang (1937), the oldest known land plant of pteridophyte aspect. In the abundant Derivation of name. From caia, Latin for cudgel, referring but fragmentary plant and animal fossils that crowd certain to the shapeof the sporangia. bedding planes, the onlyhigher plant taxa originally recorded were Cooksonia pertoni and Hostinella sp. (Lang Diagnosis. Plant in which distal region comprises smooth 1937). This contrasts markedly with the diverse rhyniophyt- isotomously branchingaxes with terminalsometimes oid assemblage described more recently from approximately bifurcating sporangia.Sporangia consistently longer thm coeval strataat Freshwater East, Dyfed (Edwards 1979). wide, with parallel sides and obtuse tips. Homosporous; However, new collections from Perton Lane have yielded a spores trilete, laevigate and retusoid. number of plants of rhyniophyteaspect, including subspecies of C. pertoni (Fanning et al. 1988), a new genus Remarks. Sporangia in Rhynia, Aglaophyton, Sporogonites with spiny discoidal sporangia(Fanning et al. 1990), new and Salopella are fusiform and unbranched. The genus Caia species of Salopella Edwards & Richardson,and further may be closer to simply branching forms of Horneophyton, plants with differentkinds of vertically elongate terminal but fossils assigned to the new genus lack any anatomical sporangia, one of which is described here as a new genus. data diagnostic of the latter. Steganotheca has an abruptly truncated sporangium with an apical thickening. Locality data and material Caia langii sp. nov. The fossils occur near the base of the Rushall Beds, just Figures 1-7 above the local equivalent of the Ludlow BoneBed Derivation of name. After W. H. Lang. (Squirrel1 & Tucker 1960). Ostracodes and spores indicative of a Pridoli age are present at this level (Kaljo & Klaaman Diagnosis. As for genus. Unbranched sporangia 2-3 times 1982; Richardson et al. 1981), the spores belonging to the longer than wide, 1.38-3.13 mm long (f = 2.07, n = 10) and lower part of the tripapillatus-spicci;la spore assemblage 0.58-1.25 mm wide (f = 0.82, n = 10) with parallel sides and zone of Richardson & McGregor (1986). obtuse apices. Sporangia bear less than 10 conical Wehave recently described elsewhere thenature of emergences with rounded apices anddecurrent bases, fossil plant preservation and the techniques employed, when 0.18-0.30mm high (f = 0.24, n = lO),0.13-0.25 mm in reporting on a new genus from the samehorizon (Fanning et diameter at base (2 = 0.18, n = 10) and 0.05-0.12 mm wide al. 1990). The present description is based on 24 coalified when parallel-sided (f = 0.08, n = 8); emergences mostly compressions. However, in those sporangia with well- concentrated on distal one-third of sporangium. Branched preserved emergences the coalified material is granular and sporangia of overall height 0.75-2.75 mm (f = 1.72, n = 4) readily fragments, whereas when emergences are apparently and 0.63-2.25 wide beforebranching (f = 1.50, n = 4). notpresent or arerepresented by traces of coal tightly Lobe length abovedichotomy 0.30-1.13 mm (f = 0.95, adhering to the sediment, the body of the sporangium often n = 4) and lobe width 0.28-0.75 mm (f = 0.52, n = 4). Axes remains intact, and can be lifted away easily, revealing an 0.18-0.75 mm wide (f = 0.34, n = 14) when parallel-sided. orange stained matrix beneath. Isospores 23-32 pm in diameter (f = 26 pm, n = 20) with 725 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/4/725/4890529/gsjgs.147.4.0725.pdf by guest on 24 September 2021 726 U. FANNING ET AL. sporangiumfound measured 1.38 mm high and0.75mm wide, the largest 3.13 mm high and 1.25 mm wide. In thefour bifurcatingspecimens, the two sporangial lobes are parallel-sided, and their lengths are less than that of the unbranched sporangia. They have similar apices (Figs 3 & 4). Theirsubtending axes tapermarkedly before becoming parallel-sided, and thus it is difficult to determine the position of sporangium-axisthe junction on morphological criteria.However, the coalified material of the sporangium is usually thicker than that of the axis. Seventeen sporangia, including branched examples, are characterized by emergences,the majority of which are incomplete (Figs 1, 2 & 3).They vary in the 3 number present,but extrapolation from a number of specimens indicates that there were probably few in the living plant. The maximum seen on anyone specimen is seven. The emergencesare mostclearly evident when preserved in profile on the sides of the sporangium. When complete such anemergence has a slightly asymmetrical, proximally attenuated, basal portion that tapers into a parallel-sided region of approximately equal length. The apex is bluntly rounded.The emergences were probably circular in cross-section. Thedecurrent basesand a few intact specimens indicatethat theemergences were directed distally,except in one casewhere the long axisis perpendicular theto sporangium surface. Incomplete examplesare variable in shape ranging fromtriangular bases to sharply truncated outgrowths. Traces of emergences can sometimes be detected on the Fig. 1. Elongated, unbranched, terminal sporangiumof Cain lungii, surface coalifiedof compressions and as coal-filled with parallel sides, obtuse tip and distal concentrationof well depressions on the underlying matrix when the sporangium preserved sporangial emergences,NMW 89.38G.1; scale bar= 0.5 mm. Fig. 2. Isolated sporangium of C. lungii with sporangial emergences seen in profile and, where granular coalified material removed, penetrating the matrix (represented by coal-filled depressions), NMW 89.386.2; scale bar= 0.5 mm. circular-irregular ambs. Trilete with narrow, low, even lips, c. 0.5 pm wide,confluent with narrowa curvatural ‘ridge’/fold of the same width.Exine laevigate, less than 1pm thick, usually crumpledand showing taper-pointed folds. Hofofype. NMW 89.38G.l.,Department of Geology, National Museum of Wales, Cardiff, Fig. 1. Type horizon. RushallBeds, Downton Castle Sandstone Formation, Downton Group, Pridoli Series. Type locality. Perton Lane Quarry, Perton Village, Stoke Edith, near Hereford (SO 5971 4035). Description. Of the 24 fertile specimens collected, 20 have elongateand unbranched sporangia with more or less parallel sides and obtuse tips (Figs 1 & 2). In 12 examples the subtending axis increased gradually in width below the sporangium so that the junction is difficult to recognize and height measurements are equivocal. They are more precise Fig. 3. Specimen of C. lungii in which the body of the bifurcating where the junction is marked by a constriction or there is an sporangium was removed intact and destroyedfor in situ spores; abrupt change in the thickness of coalified material. In two faintly preserved sporangial, emergences are seen in profile and cases, thesubtending axis is parallel-sided and slightly penetrating the matrix beneath,NMW 89.38G.3; scale bar= narrowerthan thesporangium. Six specimensare 0.5 mm. Fig. 4. Bifurcating sporangiumof C. lungii lacking represented by isolatedsporangia (Fig. 2). The smallest sporangial emergences,NMW 89.38G.4; scale bar is0.5 mm. Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/4/725/4890529/gsjgs.147.4.0725.pdf by guest on 24 September 2021 LA TE SILURIAN LATE LAND VEGETATION 727 5 Pi. 5. Reconstruction of the terminal part of C. lungii; scale bar is 0.5 mm. Pi. 6. Scanning electron micrographof in situ, trilete,laevigate, retusoid spore of C. langii NMW 89.386.5; scale bar is 7.5 pm. Fig. 7’. Scanning electron micrograph of in situ, folded spore of C. Lungii, with granular surface, NMW 89.386.6; scale bar is 8.5 pm. is removed (Fig. 2). In unbranched sporangia, emergences Lang (1920) originally described the sporangia of this are usually concentrated in the distal third of the species as bifulcate or cylindrical structures with broad flat sporangium with rare examples towards the base. Limited apical ends, and considered such organization unique among evidence suggests that they are inserted in a spiral. A typical bryophytes and vascular plants. Should such three- arrangement is shown in the reconstruction (Fig. 5). dimensionally preservedpreservedplantsbe as Seven specimens (including a branching one) appear to compressions they would certainly be comparable in gross lack any emergences (Fig. 4). These are of the preservation morphology to the new plant described here, if not in size. type where the sporangium lifts off intact and emergences Further similarities include the lack of distinction between are very poorly preserved or missing.